Making grass. Difference between hair particles and emitter?
Generally, hair is recommended because you can use Cycles particle hair options to get a decent grass shape. It can also be softer on performance due to Children. However, Emitter pulls ahead when you have a diverse set of grass objects. Load them into a Group, and have the particle system use the Group option. This gives better look and performance (assuming you have good grass assets), but requires more work to set up.

Overall, both options work and have their uses. As far as I can tell, hair is commonly recommended in tutorials because Blender Guru put out a good tutorial for Hair grass some time ago, and so the method caught on.